Many columbian and thai strains, as well as other landrace strains.
One I found:
Colombian Gold
Breeders Choice
Price: 30.00 Euros ($44.44 US)
Summary:
Pure Sativa Heirloom Colombian Gold genetics
Gorgeous pure equatorial plants
Authentic Colombian Gold High, extremely potent
10 Seeds Per Pack
Overview:
This is a heirloom line of pure Colombian 'gold' genetics. A pure Sativa F1 cross of the highest quality, comprised of two 'gold' lines from the Highlands of Colombia. Both lines are pure equatorial Sativas and this is a long flowering line for those seeking absolute quality.
The combination of the two highly selected 'golds' produces progeny that meet with the legends of old. This is a line of dreamy, wide psycoactive highs with very deep effects.
Specifications:
Sativa/Indica: Pure Sativa
Indoor/Greenhouse: 16-22 Weeks
Outdoor finish: Late December/January, 30 degrees latitude and South.
Odor level: Low
Mite resistance: High
Mould Resistance: High
Stretch: 4x and greater
Yield: High
Details:
1. Seed Lot: Created 01/05
2. Breeding History: Generation #1
3. Germination Tested: 01/07 - 90/100
4. Flowering Time: 18 - 20 + weeks approximate flowering time
.........And I think the OG Purple Haze was a 20+ wk plant.
The problem with asking "what strains take that long" is that named strains were mostly all developed for practical growing so therefore of course won't take that long.